Beam loss suppression by improvement of vacuum system in J-PARC RCS

Kamiya, Junichiro   ; Kinsho, Michikazu  ; Noshiroya, Shiyoji; Yamamoto, Kazami   

In high power beam accelerators, pressure of the beam line directly affects the amount of the beam loss. J-PARC RCS is one of the most high power beam accelerators in the world. It aims the 1MW beam power, which corresponds to the average and peak beam current of 333 A and about 10 A, respectively. In the present stage, the injection line called L3BT line (Linac to 3GeV Beam Transport line), is the section, where the pressure notably produces the beam loss. In this section, H beam from Linac was converted to H beam by charge stripping due to the interaction between H beam and the residual gas molecules. Such H beam was not bended by the injection septum magnets and directly hit the vacuum wall. We decided to add the vacuum pumps in this section to reduce the residual gas molecules in the beam line. In this paper, we will present the effectivity of the additional pumps by showing the relation between the beam line pressure and beam loss.